1. Field of the Invention
The subject of the invention is a process for the production of new shaped parts used for the production of construction material, structural material or packaging material, preferably made from wood chip and/or fibre-based sections and/or boards, also the equipment for producing the parts and the use of the said parts.
2. Description of the Related Art
Many procedures are known by means of which biopolymeric products may be broken down in order to process them in a separate, second work step into other products, e.g. wood-fibre boards. The biopolymeric products are broken down by the application of steam followed by decompression or mechanical comminution. Usually a combination of these two methods is used. The serious drawbacks of both these processing methods are that they require high inputs of energy and also that the intermediate products obtained can only be processed in batches.
Other processes are known in which a mass consisting of resin and wood chips is extruded to produce structural boards. Specially designed extruders, and especially extruder screws, have to be used for this purpose. In most cases, only semi-finished products are produced and no attempt is ever made to produce the final product in one single operation. The expense involved in having to provide separate machinery for the final products adds to the expense of the boards, wall elements, etc. which are extruded on the known machinery.
Reference is made here to German Patent Application DE-A1 1 653 263 which can stand as an example of the known extrusion processes for producing boards and sections from material containing lignocellulose. According to that Patent Application, wet raw material in the form of chips is first dried in the drying mixer to the desired moisture content then mixed with glue in at least one mixer, and only after a binder--specific materials are mentioned in the Patent Application--is applied in a separate wetting step is the raw material continuously extruded in a screw extruder while continuously adjusting the pressure and while also regulating the temperature, to form the finished product.
For the manufacture of a cigarette-like product, the concept is known of compressing a moist mixture of natural fibre-shaped material and starch in an extruder until the starch melts to form a gel which is then allowed to expand to give a foam-like product made of biodegradable substances, cf. EP-A 113 595.
Furthermore, it is known from US-A 4 357 194, that a mixture of natural fibre-shaped or fibre-containing material and starch or sugar may be compacted and heated with steam in order to obtain particle boards made from biodegradable substances, without using artificial glue (adhesives). In addition, US-A 4 627 951 describes processes by means of which natural, sugar-containing, fibre-shaped material may be compressed in heatable board-pressing machines, without steam and without the addition of glue, to obtain particle boards made of biodegradable substances.
The disadvantage of the chipboards produced by the known procedures is that they have a high density which makes them heavy and awkward to handle when they are used, for example, in the construction of small items of furniture; furthermore, they are not very well suited for use in thermal insulation applications e.g. as floor, wall and ceiling boards, attic lining materials etc.
Another large area is accounted for by the production of insulation boards--preferably of low density--from foamed plastics, which vary widely in their properties, whose porosity is obtained by gas-generating primary components or additives The disadvantages of such products are that their mechanical strength declines rapidly at low density, they melt and burn easily their resistance to chemicals is inadequate and, last but not least, they do not break down readily once they are disposed of as waste. What is more, the above-described fibre boards can also cause environmental problems right at the manufacturing stage, due to the chemicals used, as well as later when they are employed in their intended applications.